(1) Field of the Invention
The invention relates to the dielectric resonator antennas and, more particularly, to packaged dielectric resonator antennas having circular and linear polarizations and high radiator efficiency.
(2) Description of the Prior Art
Design of compact and fully integrated antennas is a major challenge in the development of modern radio frequency (RF) front end products for wireless communications. Due to natural physical limitations on the RF system dimensions, an integrated antenna has, as usual, small electrical size and must operate with a finite “ground plane”, which has a great influence on the return loss and may result in a low forward-to-backward ratio. The conventional integrated patch antennas suffer from low radiation efficiency, high sensitive fabrication tolerances, and narrow bandwidth. In particular, in Song, C. T. P. et al, “Packaging technique for gain enhancement of electrically small antenna designed on gallium arsenide”, Electronics Letters, Vol. 36, Issue 18, 31 Aug. 2000, pp. 1524-1525, an antenna system in a package consisting of a printed feed with a parasitic radiator (FIG. 1) was proposed. The antenna system in the package has the overall dimensions of 20×20×8 mm and provides linear polarization radiation at a frequency of 5.8 GHz. The drawbacks of this solution are mainly the narrow impedance bandwidth of 0.67% and relatively high return loss of −6 dB within the operating bandwidth. The paper's proposed solution also exhibits low forward-to-backward ratio (FIG. 2) that may result in a feedback to the sensitive circuitry of the RF system.
Dielectric resonator antennas have better radiation efficiency and polarization selectivity than patch antennas and even may be designed with smaller dimensions if the material of the dielectric resonator has a high dielectric constant. In particular, dielectric resonator antennas operating at linear and circular polarization with rectangular, cylindrical, conical, and hemispherical dielectric resonators have been disclosed in the following references: Petosa, A.et al, “Recent advances in dielectric-resonator antenna technology”, IEEE Antennas and Propagation Magazine, Vol. 40, no.3, pp.35-48, June 1998; Leung, K. W. et al, “Circular-polarized dielectric resonator antenna excited by dual conformal strips”, Electronics Letters, Vol. 36, Issue 6, 16 Mar. 2000, pp.484-486; Long, R. T. et al, “Use of parasitic strip to produce circular polarization and increased bandwidth for cylindrical dielectric resonator antenna”, Electronics Letters, Vol. 37, Issue 7, 29 Mar. 2001, pp. 406-408; Esselle, K. P, “Circularly polarized higher-order rectangular dielectric-resonator antenna”, Electronics Letters, Vol. 32, Issue 3, 1 Feb. 1996, pp.150-151; Kishk, A. A. et al, “Conical dielectric resonator antennas for wide-band applications”, Antennas and Propagation, IEEE Trans., Vol. AP-50 Issue 4, April, 2002, pp. 469-474; and Kishk, A. A. et al, “Analysis of dielectric-resonator antennas with emphasis on hemispherical structures”, IEEE Antennas and Propagation Magazine, Vol. 36, Issue 2, April, 1994, pp. 20-31.
However, the solutions for integrated dielectric resonator antennas in RF systems in packages have not yet been disclosed. Also, the available feed designs for dielectric resonator antennas with circular/linear polarized radiation are not convenient for the antenna integration in RF systems in packages and have some drawbacks in terms of available bandwidth and limitations on the ground plane size. For example, some of these feed designs are disclosed in U.S. Pat. Nos. 6,198,450, 6,531,991, and 6,407,718 all to Adachi et al.
In particular, for linear polarized radiation of a dielectric resonator antenna there were proposed feeds in the form of probes, printed electric/magnetic dipoles and electric/magnetic loops (Petosa et al). The drawbacks of this solution are the requirement of drilling holes in the dielectric resonator, difficulties of the antenna integration, and/or narrow impedance bandwidth achievable.
To form a circular polarized radiation in a dielectric resonator antenna it is necessary to excite at least two orthogonal modes with a phase shift of 90°. To achieve this goal in Leung et al, a feed comprising two orthogonal dipoles (electric or magnetic) is fed through a circuitry that splits equally the RF power between the dipoles and introduces an additional phase shift of 90° for one of the dipoles. The drawbacks of this solution are a complicated feed design and higher losses in the splitter (FIG. 3) and phase shifting circuitry. Also, the power splitting and phase shifting circuitry requires considerable space on the printed circuit board (PCB) and thus complicates the antenna integration into the RF system in the package. U.S. Pat. No. 5,940,036 to Oliver et al shows a single feed having two mutually orthogonal modes. U.S. Pat. No. 6,147,647 to Tassoudji et al, U.S. Pat. No. 6,344,833 to Lin et al, and U.S. Pat. No. 6,292,141 to Lim describe conductive strips formed orthogonally with respect to the ground plane to provide circularly polarized radiation in a dielectric resonator antenna (DRA).
To simplify the feed and to reduce losses, it was proposed in Long et al to use additional metallization of the resonator in the form of strips to shift the resonator frequency of the orthogonal mode, so that it would acquire the additional phase shift of 90° when excited at the frequency close to the resonant one (FIG. 4). The drawback of this solution is the requirement for the dielectric resonator metallization and difficulties in the antenna tuning to compensate for the fabrication tolerances.
To solve this problem, in Esselle et al it was proposed to use a rectangular resonator with different sides. In this case, the resonator shape may be chosen so that the orthogonal modes will have slightly different resonant frequencies thus providing an opportunity to form circular polarized radiation from the antenna (FIG. 5). The drawback of this solution is a strict limitation on dielectric resonator fabrication tolerances and a limited bandwidth for an acceptable level of the axial ratio of the antenna. U.S. Pat. No. 6,323,824 to Heinrichs et al shows a rectangular resonator mounted on a printed circuit board.